1. Field of the Invention
This invention relates to the field of tools and more particularly to the field of specialized tools for maintaining transmission lines carrying volatile fluids under pressure.
2. Prior Art
In the transmission of highly volatile liquids, such as gasoline, or in the transmission of natural gas, it is necessary to meter the flow of the gas from the source to the user. It is also often necessary to connect other elements, such as pressure-correctors, to the line for proper control and measurement of the gas flow.
Particularly in the transmission of natural gas, the index of the flow of gas is maintained in ambient air conditions but the flow information comes from a flow sensor which, at one end, is active and maintained in the environment of the fluid which is passing through the transmission lines. At the other end the sensor is coupled into the indexing or metering elements or, in some cases, into the pressure and flow rate correction mechanism. The flow sensor normally used involves a vane which is activated by the flow of gas through a metering chamber. The vane rotates at a rate related to the rate of flow of the fluid being measured. At the opposite end of the sensing device, and in an ambient air environment, there is a coupling unit, sometimes called a "wiggler" which is mechanically coupled into the pressure correcting or indexing mechanism. There is a rotary seal about the shaft which couples the two ends of the sensing element. This sensing element, in the natural gas transmission field, is referred to as an "axle box". With time, because of the rotary motion of the shaft in the axle box, the seal wears and leaking of gas through the seal occurs. This, of course, is not tolerable for two reasons. First, it is highly dangerous to permit the leakage of natural gas into any region, particularly into a basement where such metering devices are normally found. The explosive power of natural gas is well known. Second, the accuracy of the correction or of the gas flow measurement is reduced as leakage increases. For both these reasons, from time-to-time it is necessary in a gas transmission line to replace the axle boxes which are associated with the gas meters or volume-pressure correctors.
In the past, in order to replace the axle box assembly it has been necessary to completely by-pass the meter, a process which can take from one to three hours. It also requires several people to achieve the by-passing result. There also is a degree of danger involved in the complete by-pass procedure. In addition to the safety factor, the cost of the labor utilized in by-passing the meter and replacing the axle box by that process is unnecessarily and undesirably excessive.
It is further object of this invention to provide a tool assembly which will permit easy replacement of the flow sensing element in a transmission line for fluids under pressure.